1. Field of the Invention
The present invention relates to a port for injecting medicaments through an implanted catheter. More particularly, the present invention relates to a port for injecting medicaments through an implanted catheter consisting of a capsule formed by a bottom, a circumferential wall enclosing a cavity, and a pierceable upper wall closing the cavity, the circumferential wall of the capsule having an outlet opening that is shielded by a filter member and to which one end of the catheter is connected.
2. Description of Related Art.
Such ports, also called "injection members", are known (German Patent 33 09 788) and generally implanted together with the catheter. The capsule has the form of a round flat shell, the cavity of which is tightly sealed by the upper wall consisting of an elastic membrane. The upper edge of the shell is configured such that one may dispose of a maximum elastic membrane surface as the injection surface. In the plane of the bottom, the capsule has a radially projecting annular flange provided with holes for suturing the capsule to the fascia. In the above known port, the outlet opening in the circumferential wall of the capsule is in communication with a radial connecting piece on which the catheter end may be plugged. An improved connection between the port and the catheter is obtained by inserting the catheter into a connecting piece of the capsule and by clamping the same by means of a sleeve-like elastomeric clamping member that may be radially deformed by a pressure member connectable with the connecting piece and which fixedly clamps the catheter (German Patent 36 28 337).
In practical use, it often happens that the pierceable upper wall (port membrane) is not perforated with port canulas specially designed for that range of application, but that users apply conventional cannulas having a disadvantageous thickness and grinding geometry. This results in fine material chips being punched out of the elastomeric upper wall that can clog the outlet opening in the circumferential wall of the capsule or the catheter itself or which may be transferred into the blood vessels. In a subcutaneous injection device according to German Patent 36 41 107, this is to be prevented by means of a porous plug of foamed material that is covered by a metal sieve and arranged above the outlet opening, bridging the cross section of the cavity and extending in parallel to the bottom thereof. This arrangement is not permanently reliable since the plate-shaped plug of foamed material that is held in the cavity of the capsule only at its rim, may loosen due to a repeated pressing of the canula tip on the superimposed metal sieve in the capsule and may thus become leaky at the rim.
It is an object of the present invention to improve a port of the initially mentioned type such that a highly effective filter is entirely functional over long periods of time.